A 50-year-old woman developed acute hemorrhagic leukoencephalitis approximately 7 days after the onset of a benign respiratory infection. Mycoplasmal pneumonia was suspected because of Coomb's positive hemolysis, cold agglutinins, and sensitivity to erythromycin base but was not proved. Acute hemorrhagic leukoencephalitis was demonstrated by brain biopsy 24 hours after admission. The patient recovered without lasting sequelae following reduction of increased intracranial pressure by mannitol, hyperventilation, and phenobarbital and prolonged immunosuppression by plasmapheresis, steroids, and cyclophosphamide.